1. Field of the Invention
The present invention relates to a solid image pickup device having a plurality of solid image pickup elements comprising photoelectric conversion elements, a method for producing the same, and an image pickup system comprising the solid state image pickup device.
2. Related Background Art
A solid state image pickup device (hereinafter referred to simply as an image pickup device) having arranged one-dimensionally or two-dimensionally solid state image pickup elements (hereinafter referred to simply as image pickup elements) comprising light receiving areas having photoelectric conversion elements formed thereon is mounted as an area sensor on, for example, a digital camera, video camera, copier, facsimile or the like. Image pickup elements include, for example, CCD image pickup elements and amplification type image pickup elements.
An example of a circuit configuration of an amplification type image pickup device is shown in FIG. 10. The circuit of the image pickup device of FIG. 10 has in a unit pixel at least a photodiode 501 and an amplification transistor 502 amplifying optical signals stored in the photodiode 501. In each pixel, a plurality of drive lines 503 are arranged in a horizontal direction, and vertical output lines 504 and gland lines 505 are arranged in a vertical direction.
One pixel is comprised of an image pickup element as shown in FIG. 11. The image pickup element of FIG. 11 has a light receiving area 2002 formed on a substrate 2001, and a photoelectric conversion element (not shown) comprised of a photodiode 501 (see FIG. 10) is formed on the light receiving area 2002. The image pickup element of FIG. 11 further has patterns 2003 and 2004 for operating the photoelectric conversion element on the light receiving area 2002, an amplifier (not shown) amplifying charges generated in the light receiving area 2002, and the like. Generally, the patterns 2003 and 2004 are comprised of metals, semiconductors and the like and have a light blocking effect, and therefore the layout thereof is desirably arranged, as shown, such that incident light to the light receiving area 2002 is not blocked.
For receiving incident light more efficiently in the image pickup element, a variety of techniques for arranging light collecting means on the light receiving area have been proposed (e.g. Japanese Patent Application Laid-Open No. 8-321595).
The pickup element shown in FIG. 12 comprises a microlens 2210 as light collecting means. According to such a configuration, light incident to the microlens 2210 is collected toward the light receiving area 2202. An optical path for incident light is narrowed as the light receiving area 2202 is approached, and an opening having a size not so great that the opening interferes with the optical path is formed in a pattern 2205′ arranged on the surface side. The patterns 2203 and 2204 are arranged with the optical path for incident light held therebetween. The arrangement position of the patterns 2203 and 2204 is not specifically limited but in the image pickup element shown in the figure, they are designed to be arranged in a position in which they interfere with the optical path for incident light and consequently, the optical path for incident light between the patterns 2203 and 2204 and the light receiving area 2202 has its shape regulated by the patterns 2203 and 2204.
In recent years, the image pickup device (area sensor) has tended to have an increased number of pixels with a large number of image pickup elements arranged in high density. Particularly, in an image pickup device of 35 mm full size standard called a large size, an exposure device for use in production of the image pickup device should be capable of processing a fine line width and performing exposure over a wide area. However, as an area to be exposed increases, the exposure device becomes hard to ensure a uniform line width in the full area and cannot form a fine line width.
For this problem, a technique has been proposed in which a pattern designed when a fine pattern is formed on one chip is divided into several patterns, and the divided patterns are exposed in a joined fashion (hereinafter referred to as exposure in joined fashion) (e.g. U.S. Pat. Nos. 5,561,317 and 5,731,131). If a layer not required to have a fine pattern is exposed, exposure in a joined fashion is not required, but a large area may be exposed collectively by a normal exposure process. In this way, a method in which an exposure process is selectively used according to the accuracy of a pattern is called a mix and match.
Exposure in a joined fashion will be briefly described with reference to FIG. 13. FIG. 13 is a top view showing an area in which the image pickup element is formed. As shown in FIG. 13, if a large size area 2101 exists, and an image pickup element (not shown) is formed in a two-dimensional form in an area 2102 in the area 2101, for example, a desired pattern is exposed in the area 2102 by exposing two divided areas 2103L and 2103R in different steps. In this case, in an area 2105 in which the areas 2103L and 2103R overlap one another (joined area), patterns printed in the respective exposure steps are joined together, whereby a pattern with a fine line width is exposed in the area 2102 having a size equal to or greater than a size capable of being exposed with one exposure by the exposure device.
As described above, the image pickup device tends to have an increased number of pixels, and is desired to have a large number of image pickup elements arranged in high density over a wide area. Thus, a pattern exposed on a substrate becomes denser and finer.
In this way, however, there arises a problem of misalignment of a pattern formation position associated with alignment accuracy of the exposure device if a fined pattern is exposed. For example, in the image pickup element of FIG. 12, even if the position of a pattern 2203 shown in the figure is an ideal position in terms of design, the pattern is misaligned like, for example, a pattern 2203′ depending on misalignment of the exposure device exposing the pattern 2203.
If the pattern and the optical path interfere with each other, and the optical path is substantially regulated by the pattern, or the pattern does not interfere with the optical path in design but a distance between the pattern and the optical path is very small, the optical path for incident light is deformed, resulting in variations in sensitivity of the image pickup element if the pattern is misaligned. Particularly, the image pickup element formed in the joined area of the image pickup device is significantly influenced by the misalignment described above because divided patterns are individually exposed with a divisional line therebetween in different steps.